On the Optical Accuracy of the Salvator Mundi

TL;DR

This study uses physically based rendering to analyze the optical accuracy of the Salvator Mundi's orb, providing evidence that it was likely hollow and rendered with optical fidelity consistent with Leonardo da Vinci's time.

Contribution

The paper demonstrates that an optically accurate rendering of the orb in Salvator Mundi is feasible with 1500s materials and lighting, supporting the hypothesis of a hollow, transparent orb.

Findings

Optically accurate images of the orb are possible with historical materials.

Alternative solid orb theories do not match the painting's appearance.

Evidence suggests the orb was hollow and transparent.

Abstract

A debate in the scientific literature has arisen regarding whether the orb depicted in Salvator Mundi, which has been attributed by some experts to Leonardo da Vinci, was rendered in a optically faithful manner or not. Some hypothesize that it was solid crystal while others hypothesize that it was hollow, with competing explanations for its apparent lack of background distortion and its three white spots. In this paper, we study the optical accuracy of the Salvator Mundi using physically based rendering, a sophisticated computer graphics tool that produces optically accurate images by simulating light transport in virtual scenes. We created a virtual model of the composition centered on the translucent orb in the subject's hand. By synthesizing images under configurations that vary illuminations and orb material properties, we tested whether it is optically possible to produce an image that renders the orb similarly to how it appears in the painting. Our experiments show that an optically accurate rendering qualitatively matching that of the painting is indeed possible using materials, light sources, and scientific knowledge available to Leonardo da Vinci circa 1500. We additionally tested alternative theories regarding the composition of the orb, such as that it was a solid calcite ball, which provide empirical evidence that such alternatives are unlikely to produce images similar to the painting, and that the orb is instead hollow.